EL devices which utilize light emission under application of an electric field show high self-distinguishability due to the self-emission and exhibit excellent impact resistance since they are completely solid devices. Therefore, EL devices have been attracting attention for application as light emitting devices in various types of display apparatus.
The EL devices include inorganic EL devices in which an inorganic compound is used as the light emitting material and organic EL devices in which an organic compound is used as the light emitting material. Organic EL devices have been extensively studied for practical application as a light emitting device of the next generation since the applied voltage can be decreased to a great extent, the size of the device can be reduced easily, consumption of electric power is small, planar light emission is possible and three primary colors are easily emitted.
As for the construction of the organic EL device, the basic construction comprises a transparent electrode layer (an anode), a layer of a thin film of an organic light emitting material (an organic light emitting layer) and a metal electrode layer (a cathode), which are successively formed on a transparent substrate. Constructions having a hole injecting and transporting layer or an electron injecting layer suitably added to the basic construction are known. Examples of such constructions include the construction of an anode/a hole injecting and transporting layer/an organic light emitting layer/a cathode and the construction of an anode/a hole injecting and transporting layer/an organic light emitting layer/an electron injecting layer/a cathode. The hole injecting and transporting layer has the function of transporting holes injected from the anode. The electron injecting layer has the function of transporting electrons injected from the cathode to the light emitting layer. It has been known that, due to the hole injecting and transporting layer disposed between the light emitting layer and the anode, a greater amount of holes are injected into the light emitting layer under a lower electric field and electrons injected into the light emitting layer from the cathode or the electron injecting layer are accumulated at the interface between the hole injecting and transporting layer and the light emitting layer to increased the efficiency of the light emission since the hole injecting and transporting layer does not transport electrons.
FIG. 1 shows a diagram exhibiting the principle of an example of the organic EL device. As shown in this Figure, an organic EL device has, in general, a construction in which an organic EL material layer 5 comprising a hole injecting and transporting layer 7, an organic light emitting layer 8 and an electron injecting layer 9 is laminated to a transparent electrode (the anode) 2 disposed on a transparent substrate 1 and a metal electrode layer (the cathode) 6 is further laminated to the organic EL material layer 5. When an electric current is applied between the anode and the cathode, light is generated in the organic light emitting layer 8 and emitted to the outside through the transparent substrate in the above construction.
For preparing the organic EL device, a patterned transparent electrode (the anode) is formed on a transparent substrate such as a glass plate in accordance with the vapor deposition or the sputtering and an insulation film having a desired pattern is formed on the formed transparent electrode. The insulation film can be formed, for example, in accordance with the etching of a film of a polyimide resin or the lithography using a photoresist. The insulation film may be used also as the light-shielding film.
On the insulation film formed on the transparent substrate, a resist pattern layer having a rectangular sectional shape or a undercut pattern profile is formed in accordance with the lithography. The formed resist pattern layer can be used as a resin separation layer and a plurality of such layers may be formed. For example, a hole injecting and transporting layer, an organic light emitting layer and an electron injecting layer are successively formed between the resin separation layers in accordance with the vacuum vapor deposition so that an organic EL material layer is formed. A metal electrode layer (the cathode) is further laminated on the formed organic EL material layer and a light emitting portion is formed. A sealing layer is formed on the light emitting portion in the final step and a sealed organic EL device is obtained.
FIG. 2 shows a partial sectional view exhibiting the construction of an example of the light emitting portion in a conventional organic EL device. On a transparent substrate 1 having a patterned transparent electrode 2, resist pattern layers (resin separation layers) 4 having an undercut pattern profile is disposed via insulation films 3. Between the resist pattern layers, an organic EL material layer 5 (having a construction constituted with a hole injecting and transporting layer, an organic light emitting layer and an electron injecting layer which are formed successively from the side of the transparent electrode layer) having a metal electrode layer 6 on the surface is disposed. Thus, a light emitting portion is formed independently without contacting the resist pattern layers 4. On the resist pattern layer 4, an organic EL material layer 5a having a metal electrode layer 6a on the surface is formed due to convenience in the preparation although the organic EL material layer 5a is not necessary from the standpoint of the function.
The insulation film 3 in the organic EL device having the construction described above has, in general, a rectangular sectional shape as shown in FIG. 2. However, in the formation of the organic EL material layer on the transparent electrode 2 between the resin separation layers 4 and the light emitting portion by laminating a metal electrode (the cathode) on the organic EL material layer in accordance with the vacuum vapor deposition, it is difficult that the side faces of a light emitting portion are formed in a vertically flat shape due to the characteristic of the vacuum vapor deposition when the sectional shape of the insulation film is rectangular. Occasionally, the light emission becomes uneven due to the extended deposition of the metal electrode material on the side faces during the vapor deposition of the metal electrode layer or short circuit takes place due to attachment of the metal electrode material to the transparent electrode. Therefore, a problem arises in that the frequency of the formation of defect products increases.
To overcome the above problem, it is considered that a sectional shape having upper edge portions having a round shape and a width increasing towards the bottom portion is advantageous. When the insulation film has the sectional shape described above, the extended deposition of the metal electrode material on the side faces is suppressed during the vapor deposition.
In accordance with a recently developed technology, a pattern is formed with a plurality of holes having a transparent electrode layer exposed at the bottom portion, a polymer organic EL material is injected through nozzles into the holes in accordance with the ink-jet process to form organic EL material layers in the holes, and a metal electrode layer is laminated on the formed layers to prepare an organic EL device. In this technology, banks composed of an insulation film (which also works as the light-shielding film) is disposed between the holes. For this insulation film, the sectional shape having upper edge portions having a round shape and a width increasing towards the bottom portion is considered to be more advantageous than the rectangular sectional shape.
Under the above situation, the present invention has an object of providing a photoresist composition which is advantageously used as the insulation film for organic EL devices and provides an insulation film having the sectional shape having upper edge portions having a round shape and the width increasing towards the bottom portion, an insulation film for organic EL devices which is obtained by using the above composition and has the sectional shape having the width increasing towards the bottom portion, a process for efficiently producing the insulation film and an organic EL device having the insulation film having the sectional shape having the width increasing towards the bottom portion.